1. Field of the Invention
The invention relates to a method for dispensing milk portions in drink preparation machines having a milk fill level monitoring unit for a milk container, such as coffee machines with a milk container provided for preparing Capuccino. The invention further relates to a milk fill level monitoring unit for a milk container.
2. Description of Related Art
In coffee machines, producing the milk froth for the Capuccino and the heating of milk is carried out in many cases in a frothing device using the Venturi principle. A negative pressure is generated with a suitable steam jet, which sucks the milk from the supply container (milk container) via a hose system and guides it into the nozzle of the frothing device. In the nozzle, the milk is brought together with the steam and the milk-steam-air mixture leaves the frothing device and runs into the cup through a steady outlet jet. If air is added to the cold milk during the extraction, warm milk with a milk froth located thereover is produced in the cup. Without air being added, the milk can only be heated.
If too little or no milk is present in the milk container and the sequence of the milk product deliveries, in particular the Capuccino delivery in the coffee machine controller is fixedly programmed, the consumer only receives a coffee without milk or with too little milk and milk froth. For the user this is irksome since he must repeat the entire process once again to obtain a perfect Capuccino (milk product) and throw away the coffee that has possibly already been withdrawn. This means a waste of resources and also has financial implications, particularly if the consumer must pay a fixed amount for the Capuccino withdrawal, whether this be in the office area or in the restaurant area.
If the milk supply is interrupted, whether this be because no or too little milk is available, this does not form a homogeneous milk outlet jet from the nozzle during withdrawal. In addition to the first annoyance, there is the added factor that the front side of the coffee machine can be contaminated by milk, water and steam splashes.
In addition, since in most cases the milk container is not transparent, it is difficult for the consumer to monitor the fill level of the milk. The supplied milk should be stored in a cooled manner as far as possible. This is achieved in many cases with an insulating container (double-walled structure with an evacuated intermediate space) or with a small refrigerator using a Peltier element. In these devices, it is not possible to monitor the milk fill level without opening the container. In addition, this is also impractical in most cases and is frequently forgotten.
There are indeed drink preparation machines such as, for example, the “Thermoplan Tiger” from Thermoplan which have an integrated milk system with a cooled milk tank in the substructure. The device additionally has a capacitively operating milk fill level monitoring unit. Naturally however, the milk fill level in the milk tank is not readily apparent to the user of the drink preparation machine even in this case. It has additionally been found that in the event of the milk fill level monitoring unit being tripped, i.e. in the event of the capacitively operating sensor being tripped in this device, a milk dispensing process which is possibly just being executed, is not carried out completely but is prematurely interrupted.
Known from WO 97/47376 is a frothing apparatus for milk in which milk can be extracted from a milk container via a suction tube by means of a pump under the control of a microprocessor controller and can be fed to a mixing device in which the extracted milk can be mixed with steam and air and can be frothed in this manner. This frothing apparatus comprises a sensor for determining the fill level in the milk container, which sensor is disposed relative to the bottom of the milk container at the same level as a suction opening for extracting the milk, which suction opening is disposed at the lower end of the suction tube, wherein signals from the sensor can be received by the microprocessor controller.